AMOLED (active-matrix organic light-emitting diode) is a display technology for use in mobile devices, televisions and other display panels. Active matrix refers to the technology behind the addressing of pixels. As known in the art, an organic light-emitting diode typically comprises a cathode layer, an electron transport layer (ETL), an emissive layer (EML), a hole transport layer (HTL), a hole injection layer (HIL) and an anode layer. As shown in FIG. 1a, the organic light-emitting diode may be fabricated on a substrate or over a thin-film transistor (TFT). The layer structure comprising the ETL, EML, HTL and HIL is also referred to as an organic active layer. A pixel circuit of a pixel having an OLED fabricated over a TFT is shown in FIG. 2a. An image display using the pixel circuit as shown in FIG. 2a generally has a defect known as image sticking. The organic light-emitting diode can also be fabricated in an inverted fashion wherein the cathode is the first layer disposed on the substrate as shown in FIG. 1b. A pixel circuit of a pixel having an inverted OLED fabricated over a TFT is shown in FIG. 2b. In a pixel circuit comprising an inverted OLED, the organic active layer has a layer structure of HIL, HTL, EML and ETL. In fabricating the inverted OLED as shown in FIG. 1b, there are a number of technical challenges and difficulties. It is because the cathode layer is subject to oxidation and the anode sputtering process can seriously damage the underlying organic active layer. Furthermore, the operational voltage of the inverted OLED as shown in FIG. 1b is relatively high as compared to the OLED as shown in FIG. 1a. A high operational voltage could reduce the useful life of an OLED.
Normal OLEDs and inverted OLEDs have been used in a display panel. A typical display panel is shown in FIG. 3. As shown in FIG. 3, the display panel 1 has a display area 100 has an array of pixels 10. The display area configured to receive data signals from a data driver 200 and gate-line signals from a gate driver 300. Each of the pixels 10 may have a plurality of color sub-pixels. As shown in FIG. 4, the pixel 10 has three color sub-pixels 20R, 20G and 20B separately receiving data signals from data lines 221, 222, 223 and a gate-line signal from gate-line 231. The data-line 224 is for the pixels in the next column and the gate-line 232 is for the pixels in the next raw. As known in the art, each of the color sub-pixels comprises a pixel circuit as shown in FIG. 2a or FIG. 2b. 